Abstract
It is important to improve stormwater runoff quality because it is a water resource for drinking water supplies, wildlife, and groundwater recharge. Due to increasing urbanization, anthropogenic pollutants can be carried in stormwater runoff and pollute receiving waterbodies. In addition, increasing impervious surfaces due to urbanization reduces the ability for water to infiltrate into the ground to recharge groundwater aquifers. Effective stormwater management is necessary to address these issues. Tactical Green Infrastructure (TGI) is a stormwater management strategy that aims to retrofit current urban landscapes with more rain gardens to improve water quality during rain events and promote infiltration. These rain gardens are installed by volunteers. The treatment and infiltration benefits of these rain gardens are unknown because TGI design and installation projects do not go through a conventional engineering design process. In this project, the Storm Water Management Model (SWMM) software program, version 5.1, was used to quantify the treatment and infiltration benefits of these rain gardens. Simulations on different rain garden sizing, matched with different impervious land use conditions, soil media thickness, and hydraulic conductivities were performed using a 29-year climate record for Davis, CA.
The different SWMM simulation scenarios and conditions show that a rain garden can infiltrate as little as 24% of the water it receives to as much as 100%. The relative sizes of the rain garden and imperviousness fraction of the catchment area significantly impact the runoff and infiltration volumes. Using the infiltration results from 144 SWMM simulations, a spreadsheet-based calculator (TGI calculator) was created to estimate infiltration volumes and pollutant load reduction for a user-defined rain garden and catchment area. The public can use this tool to quantify the benefits of a rain garden installation.